1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and a method of manufacturing the same, and more particularly, to a liquid crystal display having reduced defects and a method of manufacturing an LCD having thin film transistors (TFTs) as switching elements.
2. Discussion of the Related Art
A conventional LCD is described with reference to FIG. 1. A gate bus line 17 is horizontally formed and a gate electrode 17a is branched off from the gate bus line 17. A data bus line 15 is vertically formed and a source electrode 15a is branched off from the source bus line 15. A TFT 8 is formed near the intersection between the gate bus line 17 and the source bus line 15. A drain electrode 15b is formed to be electrically connected to a pixel electrode 4.
The structure of the conventional LCD is described in more detail with reference to FIGS. 2 and 3, which show cross-sectional views taken along lines II--II and III--III in FIG. 1, respectively.
Referring to FIG. 2, a gate electrode 17a, which is branched off from a gate bus line, is formed on a transparent substrate 11. An anodic oxidized layer 35 is formed on the gate electrode 17a to improve insulation property of the gate electrode 17a and to prevent hillocks. A gate insulating layer 23, which is made of an inorganic material such as SiN.sub.x or SiO.sub.x, is formed on the surface of the entire surface of the transparent substrate 11 including the gate electrode 17a. A semiconductor layer 22 made of amorphous silicone (a-Si) is formed on the gate insulating layer 23 over the gate electrode 17a. An ohmic contact layer 25 is formed on the semiconductor layer 22. A source electrode 15a branching off from the data bus lines 15 and a drain electrode 15b are formed with a certain distance in between, each of the electrodes being formed on the ohmic contact layer 25. A protection layer 26, which is made of an organic material such as benzocyclobutene (BCB), is formed to cover the entire surface of the substrate 11 including the source electrode 15a and the drain electrode 15b. A pixel electrode 4 is formed of a transparent conductive material, such as indium tin oxide (ITO), on the protection layer 26 to be connected to the drain electrode 15b through a contact hole 31 formed in the protection layer 26. Reference letters A and B in FIGS. 1 to 3 show over-etched portions of the pixel electrode 4.
Referring to FIG. 3, the gate insulating layer 23, which is made of inorganic insulating material, such as SiN.sub.x or SiO.sub.x, is formed on the transparent substrate 11, and the data bus line 15 is formed thereon. The protection layer 26, which is made of BCB, covers the entire surface of the substrate including the data bus line 15, on which the pixel electrode 4 is to be formed. Reference letters A and B indicate over-etched portions of the pixel electrode 4. Due to these over-etched portions, light leakage occurs in the areas indicated by 1 and 2.
In the conventional LCDs, the protection layer 26 is formed of an organic insulating material, such as BCB, which has a good leveling property and a lower dielectric constant than that of an inorganic insulating material. Therefore, the pixel electrode 4 can be formed to overlap the data bus line 15. As a result, the aperture ratio of the LCD can be improved.
The pixel electrode 4, however, can not be formed to a designed pattern (illustrated by dashed lines in FIG. 1) in practice. This is because during the removal of indium tin oxide (ITO) by etching, etchant infiltrates into the interface between the ITO layer 4 and the organic insulating protection layer 26, resulting in over-etching of the ITO layer. The over-etched portions are illustrated by A and B in FIGS. 1 to 3. It is difficult to control these over-etched portions. Moreover, pixel electrode causes light leakage in the portions 1 and 2 of FIG. 3. Accordingly, contrast and display quality of the conventional LCD are deteriorated.
In detail, the ITO layer is over-etched by the etchant infiltrating into cracks in the ITO layer or interface between the ITO layer and the organic protection layer. The cracks are formed during depositing and patterning the ITO layer on the protection layer, due to the difference in thermal expansion coefficient between these two layers. The interface between these two layers has poor adhesion property.
Referring to FIG. 4, when the ITO layer on the protection layer 26 made of an organic material, such as BCB, is patterned to form the pixel electrode 4 using a photoresist 300, the ITO layer is over-etched by as much as amount A by the etchant (indicated by a line with arrowheads) infiltrating into the interface 200.